1. Field of the Invention
The invention relates to an alloy for producing metal foamed bodies, a process for producing the alloy with certain additives for the production of metal foamed bodies.
2. Description of the Related Art
Various processes for producing metal foamed bodies are known and consist essentially in adding a gas-producing expanding agent to an alloy powder or a powder mixture comprising alloying constituents, with an unfoamed semifinished product being produced first, after which this semifinished product is foamed by being heated to a temperature above the decomposition temperature of the expanding agent, preferably in the temperature range of the melting point of the metal alloy, after which the body which has been foamed in this way is then cooled. The foaming of the semifinished product may take place freely or inside a die, and if aluminum or aluminum alloys are used, it is possible to produce metal foamed bodies with a density of approximately 0.3 to 1.7 g/cm.sup.3.
A process for producing porous metal bodies is described, for example, in DE-40 18 360 C1 and comprises the following steps: producing a mixture from at least one metal powder and at least one gas-producing expanding agent powder, hot compacting of this mixture to form a semifinished product at a temperature at which the metal powder particles are joined predominantly by diffusion and at a pressure which is sufficiently high to prevent decomposition of the expanding agent, in such a manner that the metal particles are joined fixedly to one another and form a gastight barrier for the gas particles from the expanding agent, heating the semifinished product produced in this way to a temperature above the decomposition temperature of the expanding agent, preferably in the temperature range of the melting point of the metal used, followed by cooling of the body which has been foamed in this way.
If pure aluminum powder with an addition of 0.1% by weight of titanium hydride powder was used, it was possible to produce a porous metal body with a density of approximately 0.78 g/cm.sup.3. The typical pore size had a diameter of around 1 mm. When using a fully alloyed powder comprising an aluminum alloy with an alloying fraction of 4% by weight magnesium and 0.4% by weight titanium hydride powder, a density of 0.62 g/cm.sup.3 with a typical pore size of approx. 2 to 3 mm was achieved.
A drawback of this known process and other processes, for example that which corresponds to U. S. Pat. No. 3,087,807 A, is that the bubble formation during foaming and therefore the structure of the metal foamed body is extremely uneven. This has undesirable effects on the mechanical properties, and consequently it has already been attempted to produce a uniform foam structure by changing the alloy composition or the way in which the process is carried out. However, these
The uneven foam structure can be ascribed to uneven nucleation for the bubble formation owing to the uneven size and distribution of the silicon particles. The microstructure of an extruded section which was produced from an AlMgSi powder mixture containing 10% silicon powder is shown in FIG. 1. The silicon particles in the matrix microstructure are unevenly distributed, and their shape and size are also highly irregular.